The operation to free 12 boys and their coach from a cave in northern Thailand is running “smoothly”, the head of the operation says.
At least four boys have been brought above ground, rescuers say, although local media have put it at six.
The mission has now been paused for at least 10 hours as oxygen levels in the cave have been depleted.
Rescuers decided to go ahead with the hazardous operation on Sunday because of fears of rising waters.
The next phase will begin on Monday morning, Chiang Rai Governor Narongsak Osottanakorn said.
Divers are guiding the 12 boys and their coach through darkness and submerged passageways towards the mouth of the Tham Luang cave system.
So far it has been moving much faster than officials had earlier predicted.
The group and their families had all given their agreement that they should be moved as soon as possible, said Mr Narongsak earlier.
What is happening at the cave?
A team of 90 expert divers – 40 from Thailand and 50 from overseas – has been working in the cave system.
The BBC’s Dan Johnson, who is at the scene, said doctors went to assess the boys on Saturday and decided on a priority list, sending the weakest out first.
Getting to and from where the boys are has been an exhausting round trip even for the experienced divers.
The process includes a mixture of walking, wading, climbing and diving – all in complete darkness – along guide ropes already in place.
Wearing full-face masks, which are easier for novice divers than traditional respirators, each boy is being accompanied by two divers, who will also carry their air supply.
The toughest section is about halfway out – at a section called “T-Junction”, which is so tight the divers have to take off their air tanks to get through.
Beyond that a cavern – called Chamber 3 – has been turned into a forward base for the divers. There, they can rest before making the last, easier walk out to the entrance. They are expecting to be taken straight to hospital in Chiang Rai town.
In an indication of quite how dangerous the journey will be, a former Thai navy diver died in the caves earlier this week. Saman Gunan was returning from a mission to provide the group with air tanks.
He lost consciousness and could not be revived. His colleagues have said they “will not let the sacrifice of our friend go to waste”.
Officials had originally thought the group might have to stay where they were until the rainy season ended – that could have meant months underground.
They had also been exploring whether they could drill down into the cave, as well as scouring the mountainside for another way in.
But with the rainy season just beginning, it has become clear that the flooding which originally trapped the boys will only get worse in the coming days.
Rescuers have been desperately pumping water out of the cave, and Mr Narongsak said on Sunday that water levels inside were at their lowest levels so far.
“There is no other day that we are more ready than today,” said Mr Narongsak.